June 7, 2012 – SAUDI ARABIA – Pilgrims to the holy city of Mekkah (Mecca), Saudi Arabia must have been astonished on Tuesday afternoon, when the weather transformed from widespread dust with a temperature of 113°F (45°C) to a thunderstorm with rain. Remarkably, the air temperature during the thunderstorm was a sizzling 109°F (43°C), and the relative humidity a scant 18%. It is exceedingly rare to get rain when the temperature rises above 100°F, since those kind of temperatures usually require a high pressure system with sinking air that discourages rainfall. However, on June 4, a sea breeze formed along the shores of the Red Sea, and pushed inland 45 miles (71 km) to Mekkah by mid-afternoon. Moist air flowing eastwards from the Red Sea hit the boundary of the sea breeze and was forced upwards, creating rain-bearing thunderstorms. According to weather records researcher Maximiliano Herrera, this is the highest known temperature that rain has fallen at, anywhere in the world. He knows of one other case where rain occurred at 109°F (43°C): in Marrakech, Morocco on July 10, 2010. A thunderstorm that began at 5 pm local time brought rain at a remarkably low humidity of 14%, cooling the temperature down to 91°F within an hour. Thunderstorms often produce big drops of cold rain, since these raindrops form several thousand meters high in the atmosphere, where temperatures are much cooler than near the surface. Some drops even get their start as snow or ice particles, which melt on the way to the surface. Additional cooling of the drops occurs due to evaporation on the way down. However, in the case of the June 4, 2012 Mekkah storm, I think the rain was probably more like a hot shower. Thus, the thunderstorms’ raindrops would have been subjected to 100 seconds of some very hot air on the way to the surface, likely warming them above 100°F by the time they hit the ground. With the air temperature a sizzling 109°F (43°C) at the time of the June 4 thunderstorm in Mekkah, the raindrops could easily have been heated to a temperature of over 105°F (41°C) by the time they reached the surface! On Saturday, June 2, the temperature in Mekkah hit 51.4°C (124.5°F), a new record for the city, and just 1.1°F (0.6°C) below the all-time hottest temperature record for Saudi Arabia (125.6°F, or 52°C, recorded at Jeddah on June 22, 2010.) I expect that 20 – 40 years from now, we’ll begin seeing occasional cases where rain falls at a temperature above 117°F (47°C) in the desert regions of North Africa and the Middle East. –Wunderground
contribution by Lilia M. B.